1. Field of the Invention
The present invention relates to a method of fabricating a field emitting tip and a field emitting tip made by such a method. The field emitting tip of the present invention can be employed in a flat panel display.
2. Description of the Prior Art
A flat panel display (FPD) can include a number of field emission devices (FED). Various fabrication techniques for manufacturing a cathode used in a FED have been proposed when manufacturing a FPD including a FED.
FIG. 1 illustrates the structure of a conventional FED. An anode plate 10 is provided to receive electrons 20 from a cathode 30. A metal ring 40, which focuses the electron emission, is provided.
FIGS. 2(a)-(f) illustrate a conventional process of manufacturing cathode 30 as shown in FIG. 1. The process begins with a bare silicon substrate 50. To form a cap 60, a small layer of SiO.sub.2 is deposited on the silicon substrate and then a layer of Si.sub.3 N.sub.4 is provided thereon. As shown in FIG. 2(a), the layers of SiO.sub.2 and Si.sub.3 N.sub.4 are patterned and subjected to a reactive ion etch (RIE) to form cap 60 for the field emission tip of the device.
An isotropic silicon etch is performed to remove a portion of silicon from the surface of substrate 50. As illustrated in FIG. 2(b), cap 60 protects part of silicon substrate 50 from the etch and a pyramid structure 70, which is a characteristic of the prior art field emission tip, is produced.
As shown in FIG. 2(c), after pyramid structure 70 is formed, portions of silicon surrounding the pyramid are etched. Thermal oxidation is then performed to sharpen the field emission tip, which leaves an oxidation layer 80.
As shown in FIG. 2(d), an insulating layer 90 is then deposited to a desired thickness by evaporation. After insulating layer 90 is formed, a mask material 120 is laid down and patterned to define the array edges and metal 100 is deposited to form a metal ring 110.
Finally, as shown in FIG. 2(f), mask 120 and cap 60 are removed along with the material formed on cap 60 and mask 120 during the process to form the field emission device having metal ring 110.
Hyung Soo Uh and Jong Duk Lee, "New Fabrication Method of Silicon Field Emitter Arrays Using Thermal Oxidation," J. Vac. Sci. Tech. B 13(2) pages 456-60 (1995) describes a similar process using a well region formed in a semiconductor substrate. FIGS. 3(a)-3(f) illustrate this process, where FIGS. 3(e) to 3(f) illustrate the overlying structure being lifted off by etching the oxide surrounding the tip using a buffered hydrofluoric acid (HF) solution.
These conventional processes to produce a field emitting tip, however, suffer certain deficiencies. For example, because the conventional processes use a thermal oxidation process to sharpen the tapered profile of the silicon field emitting tip, the processes are time consuming. Further, the thermal oxidation process is not easy to control and, thus, the degree of sharpness of a tip may be degraded due to uncertainties based on the degree of oxidation. Also, cap 60, which functions as a hard mask during the processes, may fracture if processing is not carefully controlled. As described, for example, in U.S. Pat. No. 5,753,130, a special kind of micro-sphere hard mask can be used in the formation of sharp tips in an attempt to alleviate this problem, but providing a special mask is undesirable.